Engines (e.g., vehicle engines) may have an ignition system for starting. Generally speaking, the ignition system includes a battery that is connected to a primary coil of a step-up transformer and an ignitor switch. When the ignitor switch is closed, current flows from the battery to the primary coil. After some period, the switch is opened and the current from the battery to the primary coil is abruptly stopped. The abrupt change in current through the primary coil causes a large transient voltage across the primary coil. The transient voltage is stepped up through the transformer and because the secondary coil is in series with a spark gap, the voltage at the secondary coil produces a spark at the spark gap. In some situations, however, it is desirable to turn off the current in the primary coil (i.e., shutdown, de-energize) without creating a spark at the spark gap.